1. Field of the Invention
This invention relates to memory systems and, more particularly, to systems for globally resetting the state of the memory cells in a memory system or subsystem to zero and to systems for detecting that all of the contents of a memory system or subsystems are in the zero state.
2. Prior Art
A memory device refers to a circuit which is used to store and retrieve information in binary, or digital, form. A memory system is a collection of memory devices. The devices are often arranged as an array of memory devices, or memory core elements, to form a memory array. A global reset for a memory system is defined as a condition in which every memory element is reset to a predefined logical zero state. A zero detection function is defined as a function which determines if every element in the memory array is in the reset state, or the logical zero state. A zero detection function is true if every memory element is in the reset state. A non-zero detection function is defined as follows: if one or more memory elements in a memory array are in a set state.
Often times, memory systems do not provide a global reset function. In addition many systems do not provide a test function to determine if the entire memory array is reset to zero state. Those memory systems which do implement a global reset function usually do so by using sequential write operations to write in zero values to all of the memory cells. Consequently, the minimum time required for the global reset function to be accomplished is the product of the number of memory addresses times the minimum write cycle for each cell. This type of memory reset function requires some form of control circuitry external to the memory to increment the memory addresses and write a zero into each memory cell.
Systems for determining other cells of a memory system are reset are required to sequentially read each memory cell and to determine if each memory cell is at a zero state. If one or more memory cells are in the non-zero state, then the all-zeros state function is false. The time required to test for all zeros in the memory cells varies, dependent upon whether the function for determining whether non-zeros are present and satisfied. The maximum time required to test for all zeros is the product of the number of memory addresses times the minimum read cycle time for the memory array.
The various techniques discussed for global reset and testing for zero states requires multiple read/write cycles for a memory.